Metal sawing machine with arcuate cut



June 16, 1931.- J. BABIN ET AL 1,810,745

METAL SAWING MACHINE WITH ARCUATE CUT Filed Oct. 6 1925 Patented June 16,1931

' cutting stroke. In fact, due to the varying est-ms,

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"Gur present inventiongre'lates. to metal sawing machines" inwhich a reciprocating saw engages the-work at a varying angle, each of the teeth ofthe blade being causedito operate thereon in afgiven portion of the arcuate cutting path. 4 V r f One particular machine of this type has been disclosed in the application for United States Letters Patent, filed May 31, 1923, Ser.

Hitherto these machines have been provided with the same kindv of saw blades as machines with rectilinear cut, that is to say blades with saw teeth arranged uniformly in the same direction. I

- Now experiments have shown that these saw blades when applied to arcuate'cutting, do not operate efliciently by reason of the curvature of the cutting path, and that they wear only upon the half of their length, viz,

that corresponding to thesecond half of the inclination of the saw blade, the normal'component acting to make the saw bite is much greater during the'second half of the working stroke than during the first half.

We have discovered that it is possible to obviate this disadvantage by replacing the saw blades with uniform teeth by blades in i which the two halves are toothed in opposite directions; it is found then that the amount of wear is regular and that it is unnecessary toweight or load up the saws. They can therefore be given for equal worka thickness less than that of the blades usually employed, this alteration resulting in the reduction of the proportion of waste. I

These saw blades, working both on the for} ward and on the return cuts, under'a small loading, do not require any'lifting or relieving device; this allows simplification ofithe machine to which they are'to be fitted. o

It has already been proposed to provide wood, sawing machines having mechanical feed, with saw blades toothed 1n one direction for half their length and in the opposite direction for the other half; but that p 10- posal had merely for its object to obtain saw blades cutting in both directions and thus to preventexcessive pressure upon the saw i. The saw is, subjected on the ing produced during stroke, while tometal sawing machines cutting in an arcu ate or curvedpath; v y p The accompanying drawing shows by. Way of eirampie one way of carryi-n-g'out the .presentinvention. t Figure 1 represents, a sa w,-Iprovided with this form of blade, inposition at the-middle of'its stroke. o Y l-- f j- --,Figure"s.2,f=3, 4 and;5 indicate the positions successively; occupied by the saw during its reciprocating movement; H Figure 6 isa modification of Figure l on a larger-scale. H v P i Referring to Figure 1-, it will be seenthat the teethvofthe saw blade at arearranged in the following, mann erfl: the teeth 5 situated to the left ofthe centre-line m n are formed shownin the drawin-gjbut di-fliering-according t'o-ltheftypeof machine, the saw frame dlis guid'edyin su'ch av-way that theblade a operates upon the'bar'to be out, as fat a varying; angle} so that the cut assumesthe shap'e-ofthe'arc z. a a onehand to a vertical force, always in the same direction,

.du'epto; thie' weightv of the mounting, andjon the -other.hand to the horizontal driving ;,force,-, which-changes; direction at every I stroke. The resultant R" ofthese forces: is

inclined in relation-to the vertical, from the direction opposite to that-of the movement of the saw. ,ltlcan be resolved in its turn intoatwo' other forces, one along the blade, 7

the other perpendicular-to the blade; this second on'ormlal. component acting'alone to makethesawbite P 1 a New at the-beginning of theaicrwara stroke (Figure 2), the resultant It being nearer to the tangent to the curve a: 3 2 than at the end of this stroke (Fig. 3) by reason of the curvature of the path, the component along the normal to this path must be far greater during the second half of the stroke than during the first half.

In the first phase (Fig. 2), the half of the saw teeth which follows the path of the cut is turned oppositely to its working direction and therefore slips easily over the metal, the normal component having a low value.

In the second phase '(Fig. 3), on the contrary, the teeth in the other half of the saw blade strike the work in their cutting direction and bite hard, the normal component of the forces exerted upon the saw' being then greater than in the previous phase.

During the return stroke (from right to left in the drawing), the same effects are reproduced in the inverse manner.

At the beginning of this stroke, the saw occupies the position of Figure 4, and its teeth slide along the portion ye of the cutting arc, the normal component of the forces being then at its minimum value.

During the end of the same stroke (Fig. 5), the teeth of the right half of the saw bite into the portion 0a 3 of the cut, the normal component of the forces being at its maximum.

Thus, in both directions, the saw slips during the first half of its stroke whereas it works during the second half and always in the most favourable conditions, without it being necessary to have recourse tora special treme teeth make with this same curved line.

The cutting action of the teeth is thus in inverse ration to the force which presses the saw against the work; this eases the duty of the extreme teeth, regularizes the wear, and allows of increasing the speed of sawing.

What we claim is:

A reciprocating saw machine for the sawing of metals comprising a rectilinear saw blade having its two halves toothed in oplifting device with a view to preventing the saw blade from rubbing too hard upon the work when it is travelling oppositely to its 7 working direction.

It is to be noted however that the force which is exerted normally to the blade, small at the start of each active halfstroke, increases during this half-stroke and attains its maximum at the end of the stroke.

If the teeth of the blade are arranged'uniformly as in the example of Figure 1, the saw, biting at each instant according to the normal force to which it is subjected, will do more work towards the end of each active half-stroke than at the beginning, and the wear upon the teeth will therefore be not absolutely regular.

This can be remedied by giving the cutting faces of the teeth, in relation to the edge of the blade, an inclination increasing from the middle of the blade towards its extremities, the directions of these faces thus tending to converge upon a point beyond the back of the blade, instead of being parallel. The teeth which are in engagement at the beginning of an activehalf-stroke will then make with the cutting path (to which the blade remains constantly tangential) an angle 0c greater than that (al) which the ex- 

